Heavy quark physics at the LHC and elsewhere

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Heavy quark physics at the LHC and elsewhere

• Guy Wilkinson
• University of Oxford
• Edinburgh, February 2006

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Talk Roadmap
Motivation context

• Why quark flavour physics?
• And why flavour physics in the LHC era?
• What is the CKM model, and what state is it in?

B-physics precision tests of the CKM triangle
beyond
The Tevatron and the LHC (especially LHCb)
We will concentrate on these
Super B-factories potential and prospects
Beyond the bs flavour physics in the charm
kaon sector
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Why do we care about flavour physics?
Quark flavour physics at heart of many of HEPs
big questions
Complementary to direct searches for new physics
at the LHC

• Powerful way to look for new physics

• Elucidate flavour structure of
• the new physics when found
• (not dissimilar to ILC)

new particles?
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Unitarity Triangle, Summer 2005
Remarkably self-consistent certainly the CKM
model is the dominant mechanism of CP violation
in nature! This conclusion is only possible
thanks to work of B factories.
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What is the CKM Model ?
In Standard Model, charged-current quark-coupling
described by the CKM matrix, which has 4
parameters, 1 of which is complex
Wolfenstein parameterisation A, ?, ? and ?.
Non-zero value of ? is source of all CP violation
in the Standard Model.
VCKMVCKM 1 implies
This is the unitarity triangle
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Existing triangle measurements the essentials
A lot of information in these ?-? plane plots!
For clarity lets focus in on most important
experimental constraints.
B
G
In (rough) order of importance

• Side B fixed by ratio of b?ul?/b?cl? (theory
  limited)

• Angle ß from measurement of CP asymmetry in
  Bd?J/?K0

• Side G constrained by measurements (limits) on
  Bd(s) mixing

• Recent B-factory results give first indications
  on a and ?

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Good agreement, but hints of inconsistencies
Overall consistency of measurements is
impressive. A closer look, however, reveals
that agreement is not quite perfect.
Indirect 0.7910.034
Direct 0.6870.032
gt2 sigma difference
Although at 1st order the CKM description is
vindicated, are there 2nd order corrections
from New Physics contributing?
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Generic Strategy to Hunt for New Physics
New heavy particles (eg. sparticles) if they
exist, are expected to lurk in box and Penguin
processes. Here contributions may be comparable
to, or exceed, the Standard Model amplitudes
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Time line of B physics facilities and goals
B-factories
Tevatron
Selected list of most important aims (in order
of likely achievement)
(double existing data set)
LHC

• Improved measurements of ?

• Observation of Bs mixing

2008

• Very high precision sin2ß

2010

• Precision measurements of ?

• Measurement of Bs mixing phase

Super B-factory

• Observation of very rare decays

Study prospects in a few of above
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Time line of B physics facilities and goals
B-factories
Tevatron
Selected list of most important aims (in order
of likely achievement)
(double existing data set)
LHC

• Improved measurements of ?

• Observation of Bs mixing

2008

• Very high precision sin2ß

2010

• Precision measurements of ?

• Measurement of Bs mixing phase

Super B-factory

• Observation of very rare decays

Study prospects in a few of above
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Bs Mixing
Next important constraint on triangle likely to
be mixing side
? Vtd/Vts
Vtd,ts
Measure ?md (slow) ?ms (fast!), frequency of
oscillations. Ratio of frequencies, with
hadronic correction (error 6) ? Vtd/Vts
?md known. Present 95 CL limit on ?ms
is gt 16.6 ps-1 (LEP/SLD alone gt14.5 ps -1)
Standard model expectation
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Bs Mixing the experimental challenges
Bs mixing search now being spear-headed by CDF
and D0.
Immediate challenge is to accumulate
enough events. Two choices

• Fully hadronic Bs
• decays, eg. Bs?Ds?
• 2) Semi-leptonic, eg. Bs?Dsl?

But we also need to tag Bs, to know flavour at
time of birth. Reduces effective statistics by a
lot! eg. eeff 1.6 at CDF.
2) has higher yield and dominates present
results but worse proper time resolution will
limit performance at high ?ms.
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Bs mixing future prospects
Present Tevatron analyses use 400-600 pb-1 of
data. More data, and improved analyses, will give
real possibility of observation (if within
Standard Model region!) soon-ish.
If the Tevatron fails, LHC should do the job.
eg. LHCb

• Can observe ?ms40 ps-1
• with 1/8 year of running.

• Sensitivity up to ?ms68 ps-1
• in one year of running

Of course this assumes aligned and understood
detector etc
Place your bets now for winner!
(4-8 fb-1 expected by 2009)
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B-physics at the LHC
LHCb
B physics advantages of LHC vs Tevatron

• 10x higher b-production cross-section
• Higher luminosity (ATLAS/CMS)
• One dedicated B-physics experiment

ATLAS/CMS excellent B-physics for channels
involving leptons
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B-physics at the LHC vs the B-factories
e?e? ? ?(4S) ? BB PEPII, KEKB pp?bbX (vs 14 TeV, ?tbunch25 ns) LHC (LHCbATLAS/CMS) pp?bbX (vs 14 TeV, ?tbunch25 ns) LHC (LHCbATLAS/CMS)
Production ?bb 1 nb 500 ?b ?
Typical bb rate 10 Hz 1001000 kHz ?
bb purity 1/4 ?bb/?inel 0.6 Trigger is a major issue ! ?
Pileup 0 0.55 ?
b-hadron types BB (50)B0B0 (50) B (40), B0 (40), Bs (10)Bc (lt 0.1), b-baryons (10) ?
b-hadron boost Small Large (decay vertexes well separated) ?
Production vertex Not reconstructed Reconstructed (many tracks) ?
Neutral B mixing Coherent B0B0 pair mixing Incoherent B0 and Bs mixing(extra flavour-tagging dilution) ?
Event structure BB pair alone Many particles not associated with the two b hadrons ?
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LHCb Spectrometer
collision point

• Crucial for B physics
• optimised geometry and choice of luminosity
• trigger efficient in hadronic leptonic modes
• excellent tracking and vertexing (?m, ??)
• excellent particle ID

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LHCb VELO (Silicon Vertex Locator)
VELO is laid out as a series of R and F measuring
stations approaching 0.8 cm to the beam line,
situated in vacuum chamber (inside beam-cavity!)
VELO key to LHCb physics programme

• Provides lifetime trigger which gives
• high efficiency for all decay modes

• Gives excellent proper time resolution
• vital for high performance Bs physics

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Example of LHCb RICH in action

• RICH sytem will allow clean separation of
  different B?hh
• modes. Not possible elsewhere at hadron colliders.

Situation at Tevatron
CDF data
Bs?KK signal
Bd??? signal
Bd??? signal
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Towards a precise measurement of ?
LHCb has a wide variety of strategies for
measuring ?
1) Tree level methods vital for benchmarking
entire triangle
Example approaches involving B?DK decays
2) Methods involving loops sensitive to new
physics
Example two-body modes
Such redundancy is essential in the hunt for new
physics!
How well do we need to do? Well 1) suggests that
we make measurement with precision equal to or
better than that from indirect prediction
? (61.4 6.5)
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B? ?DK - interfering B diagrams
Two interfering tree diagrams (theoretically
clean).
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B? ?DK - some specific examples
LHCb aspects particularly suited to B?DK trigger
RICH
Statistics in recent B-factory publications
Expected annual yield at LHCb
Do decay mode
CP-self conjugate (3-body Dalitz)
Ks?? (KsKK)
200
5000
CP-eigenstates (GLW)
8000
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KK (??)
Doubly Cabibbo suppressed (ADS)
K? (K???)
10
2000
Lack of tagging requirement means full statistics
can be used!
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Example of B?DK analysis D(Ks??)K
Pioneered by B-factories look at Dalitz space of
D decay products for B and B- decays. Rich
resonance decay structure allows for reasonable
sensitivity with 200 events.
B-factory samples have statistical error of
20o. Scope for 5o LHCb error, but needs good
understanding of D decay model
Other approaches (eg. ADS) cleaner and more
precise.
All DK methods measure same parameters, but have
differing systematics ? combine for final
precision of 1o ?
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Accessing ? with B?hh Decays
Penguin
Tree
(Recall role of RICH in separating modes)
?
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Accessing ? with B?hh Decays
For both decays measure ACPd,s Ad,scos?md,st
Bd,ssin?md,st
Large event yields, RICH and good proper time
resolution allow for good precision on all
parameters.
Bd ???
Suitable combination of parameters gives ? to 5o
Hadronic amplitude which we assume to be same
for two cases
Enough constraints exist in analysis that
stability to U-spin symmetry assumption can be
assessed.
Bs?KK
Comparison with tree-level measurements a very
important test!
? degrees
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Beyond the triangle 1 the Bs mixing phase
Other angles exist beyond those of familiar
unitarity triangle ! At order ?3 CKM element Vts
is real at order ?5 it has a very small phase, c
, (c ? 0.02 radians). Phase accessible through
Bs mixing.
Analogous to ß measurement in B0 system ( Vtd).
In Bs case, new physics contributions may
be much more evident, because of tiny SM signal !
Golden channel for c Bs?J/?F. Every LHC
experiments expect 50-150k events.
Vector-vector final state ? angular
analysis needed to separate CP-odd and even
amplitudes.
LHCb is sensitive at level of SM expectation,
but may need several years for 5s observation.
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Beyond the triangle 2 very rare decays
In addition to studying consistency of triangle,
we may look for certain B decays heavily
suppressed in Standard Model.
Clean Standard Model prediction
Br (Bs ? µµ-) 4 10 -9
Large enhancements possible, eg. MSSM
Br tan6ß / M2H !
1 year Bs ? ? ? signal (SM) b??, b??background
LHCb 2 fb1 17 lt 100
ATLAS 10 fb1 7 lt 20
CMS (1999) 10 fb1 7 lt 1
Distinctive leptonic signature good for all
experiments
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Motivation Prospects for a Super-B Factory
Spectacular success of BaBar/Belle demonstrates
power of Upsilon(4s) environment. Aim for order
in magnitude improvement in precision
Two proposals SuperKeK Frascati. Briefly
discuss former.
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Projections for luminosity at SuperKEKB
Design lumi 4 x 1035 cm-2 s-1
Aim for 100x present yield
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SuperBelle detector
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Decays with neutrinos, ? and ?0s feasible

• B decays with neutrinos
• B g Dtn, tn, uln
• B decays with g, p0 B g Xsg, p0p0 etc.

Not possible at LHCb ! Methods established at
BaBar/Belle.
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What can a Super B-factory do?
Pursue hints of new physics seen at BaBar/Belle
which are difficult to pursue at LHC
Central values as now, with Super-B precision
Example sin2ß measured with J/? Ks and FKs
B0 g J/?Ks
b?FKS has b?s Penguin
sin2ßJ/?K0 0.69 0.03
B0 g fKs
sin2ßFK0 0.47 0.19
Mode unsuited to LHCb (poor vertex constraint)
(0.03 stat error on ?sin2ß)
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More to quark flavour physics than Bs !
All discussion so far has focused on B decays.
Why is this?
Because in B system there is a multitude of
observables that can be cleanly related to CKM /
SM predictions
But there is still much to learn from other quark
systems

• D0 system very small mixing and CP violation
  expected.
• New physics may couple differently to up-type
  quarks !

• Kaon system historical view is that despite
  being birthplace
• of CP physics, interpretation of measurements
  is messy.
• Not always true !

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New opportunities in charm physics
Mixing and CP violation expected to be small in
Standard Model, but are coming within range of
new experiments, eg. LHCb and SuperBfactory.
Clear signatures can be looked for. For
instance, for direct CP violation compare D0 and
D0 decays to CP eigenstates, such as KK, .

??
Current precision 10-2. In SM we expect effects
of order 10-3.
LHCb will accumulate 5 x 108 D?D0(hh)
p.a., gt100x Tevatron yields.
?
Clear discovery potential!
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K???? and the unitarity triangle
Two ultra-suppressed kaon decays provide
extremely clean constraints on unitarity
triangle. Standard Model predicts
Irreducible theory error on ?0?? 1 on ???
5
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Decay already observed! 3 events at E787/949
(now defunct) Rate consistent with SM.
P-326 proposed CERN experiment (in NA48 hall)
Data taking in 2010
With 100 events !
Reconstruct missing mass. Vetoes vital!
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Prospects for K0??0?? E391a at KEK
First dedicated K0???? experiment. Challenging
signature!
Requirement for selection

• 2 photons only
• Missing pt

No events !
missing pt (GeV/c)
z position of vertex (cm)
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Prospects for K0??0?? upgrade for J-PARC
E391 aims to reach 10-9 (Grossman-Nir limit) with
present data.
E391 situated on 12 GeV KEK PS.
Upgraded experiment planned for J-PARC (30 GeV
protons) ? 100x KL flux
Intention is to have sensitivity at SM BR.
3 years of operation
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Conclusions and Outlook
Now know that observed CP violation is described
to first order by CKM model. But still expect
new physics to show!
Augment existing triangle constraints with new,
very precise measurements involving tree and
loop
Bs mixing ? (tree and loop)
Additional measurements beyond the triangle
Bs mixing phase very rare decays (eg. Bs?µµ)
LHC studies can be complemented by super-clean,
super-B !
Charm and kaon mesons still have role to play.
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Backup Slides
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Choice of Geometry and Running Luminosity
Forward spectrometer geometry exploits correlated
production (excellent for flavour tagging)
De-focus beams locally to lower luminosity to 2
x 1032 cm-2 s-1
Inelastic pp collisions/crossing
Optimises fraction of 1-interaction events ?
cleaner to analyse. Also allows for acceptable
occupancy and radiation levels.
Forward layout also allows planes of silicon to
approach very close to beam
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Trigger

• sbb 500 mb, lt 1 of inelastic cross-section
• Use multi-level trigger to select interesting
  events ? high pT electrons, muons or hadrons
  ? vertex structure and pT of tracks ? full
  reconstruction

200 Hzto tape in exclusive decays
? ? ?
3060efficiency
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LHCb Ring Imaging Cherenkov (RICH) System
PID mandatory for suppressing same topology
backgrounds in many final states, and for adding
kaons to flavour tagging.
Wide momentum span in PID requirements ? 2 RICHes
with 3-radiators
Cherenkov rings in RICH 1
Good performance for 2ltplt100 GeV/c